Touch screen displays are commonplace in today's commercial electronic devices. Such displays are finding widespread use in many new products, such as cellular phones, personal digital assistants (PDAs), camcorders, and laptop personal computers (PCs). Touch screen displays can be configured with either a finger touch input and/or a stylus (or “pen”) touch input. Over the years, a number of touch detection technologies have been developed that allow the touch screen display to accurately identify the location of the touch on the display screen.
Traditionally, one such technology utilizes capacitive touch panels that identify the point of the touch using sensors that detect changes in electrical current generated by contact with a finger and/or stylus that change the electrostatic capacity (e.g., load). There are two types of capacitive touch panels: surface capacitive touch panels and projected capacitive touch panels. In surface capacitive touch panels, electric voltage is applied to electrodes positioned in the four corners of the glass substrate, generating a uniform low-voltage electrical field across the entire touch screen display screen. The coordinates of the position at which the finger touches the screen are identified by measuring the resulting changes in electrostatic capacity at the four corners of the panel. In projected capacitive touch panel, a layer of transparent electrodes is positioned with the electrodes in a specific pattern and the surface is covered with an insulating glass or plastic cover. When a finger approaches the surface, the electrostatic capacity among multiple electrodes changes simultaneously, and the position where contact occurs can be identified by measuring the ratios between the electrical currents.
Unlike a finger touch that allows the capacitive touch panels to leverage the conductive properties of human body to detect a change in the screen's electrical field, however, the touch screen displays are unable to leverage the touch of a stylus to accurately identify the stylus touch. To address this problem, the touch screen displays may also separately use a “digitizer” to enable communication between the touch screen display and the stylus and the user touch. The digitizer is a component used to convert analog signals into digital signals. In the context of the touch screen displays, the digitizer may measure self-capacitance to detect and convert user actions (e.g., touch, swipe) into a digital signal that could processed by the electronic device associated with the touch screen display (e.g., tablet, laptop, mobile phone).
Many touch screen displays produced today that utilize capacitive touch panels, however, rely on the touch layer to be sandwiched between a display panel (e.g., the panel producing the images for display) and a cover layer (e.g., glass or plastic layer), adding to the overall width of the screen. With the drive to reduce the size of the consumer electronic devices, display manufacturers have developed “in-cell” touch system that generally refers to the implementation of touch sensors that are physically inside the cell of a display panel. While this removes the need for the touch layer to be a separate layer from the display panel, such integration raise other challenges, including challenges with respect to accurately detecting stylus touch.